1. Field of the Invention
The invention relates to diazotypy and more particularly relates to methods and compositions for developing diazotype materials.
2. Brief Description of the Prior Art
Diazotype materials and processes have been widely described in the literature; see for example the text "Light Sensitive Systems", J. Kosar, John Wiley and Sons Inc., N.Y., N.Y. (1965).
In general, diazotype prints are obtained by an imagewise exposure of a light-sensitive diazo material to ultraviolet light followed by development of the exposed diazotype material. There are several different methods available to develop the latent image imposed on the light-sensitive diazo material by the light exposure. The following image development methods have found commercial application:
(1) ammonia development; PA0 (2) amine development; PA0 (3) thermal development; and PA0 (4) moist (liquid) development PA0 1-diazo-2,5-dibutoxy-4-benzolyamino benzene, chloride 1/2 zinc chloride (Diazo 22*), PA0 1-diazo-2,5-dimethoxy-4-p-tolylmercapto-benzene chloride 1/2 zinc chloride (Diazo 32*), PA0 4-diazo-2,5,4'-trihydroxy diphenyl oxalate (Diazo 42*), PA0 1-diazo-2,5-diethoxy-4-p-tolymercapto-benzene chloride 1/2 zinc chloride (Diazo 72*), PA0 1-diazo-3-ethoxy-4-[N-benzyl-N-methylamino]-benzene chloride zinc chloride (Diazo 74*), PA0 1-diazo-3-chloro-4-N,N-dibutylamino-benzene borofluoride (Diazo 75*), PA0 1-diazo-2-chloro-5-(4'-chlorophenoxy)-4-N,N-diethyl aminobenzene chloride 1/2 zinc chloride (Diazo 78*), PA0 1-diazo-2-chloro-5-(4'-chlorophenoxy)-4-N,N-dimethyl aminobenzene chloride 1/2 zinc chloride (Diazo 79*), PA0 1-diazo-3-chloro-4-N-methyl-N-cyclohexylamino-benzene chloride 1/2 zinc chloride (Diazo 87*), PA0 1-diazo-4-(N-ethyl-N-benzyl) amino-benzene chloride 1/2 zinc chloride (Diazo 14*), PA0 1-diazo-2,5-dibutoxy-4-morpholino-benzene chloride 1/2 zinc chloride (Diazo 54*), PA0 1-diazo-3-chloro-4-N,N-diethylamino-benzene chloride 1/2 zinc chloride (Diazo 77*),
All of the methods have had advantages as well as certain shortcomings or inconveniences. For example, the ammonia development process requires the handling of liquid or anhydrous ammonia. Even if the developing machine fully contains the ammonia vapors, some residual ammonia adheres to finished prints and releases therefrom, inconveniencing the environment. Amine development, as described for example in U.S. Pat. Nos. 3,446,620; 3,349,908; 3,578,452 and 3,809,559 overcomes many of the problems associated with ammonia development, but fresh prints released from the processing apparatus have a tacky surface imparted by the alkaline amine, with a resulting unpleasant feel to the skin. In addition, "ghost" printing occurs. This consists of a repeat image transferred to the activator transfer roller from the print dye. Also, print backgrounds tend to discolor after short storage periods. This is very pronounced in blackline diazotypes developed with amines. Another inconvenience is due to volatility of even high boiling amines. Following prolonged use of the development equipment the amine evaporates into the atmosphere and then deposits on cold surfaces in the room. The volatilized amines also usually possess an undesirable odor.
Diazotype prints developed by thermal development methods suffer from serious shelf life problems unless the paper is not only kept very dry but also at low storage temperatures. Thermally developed diazotype prints also release volatiles into the surrounding atmosphere, at the elevated development temperatures encountered.
Moist or liquid development is probably the oldest commercial diazotype developing process and is used to develop the so called "one component" diazotypes. Such reprographic diazo material contains besides stabilizers and other additives, the light sensitive diazo compound. No coupler is present with the diazo compound. After imagewise exposure, the diazotype surface is contacted with an aqueous developer containing one or more couplers and buffer salts to neutralize the stabilizers in the diazotype layer. The coupler reacts with the diazo compound to generate print dye development. The method is not without disadvantages. As the water in the developer solution penetrates the print surface, it tends to swell the cellulosic fiber of the diazotype base paper. Later on drying, shrinkage occurs and results in a curling of the print. To overcome the curl problem, liquid development machines have been made which apply developer to both sides of the sheet and thus balance fiber swell and shrinkage. Also, diazo prints processed by moist development pick up a total of approximately 20 gms of water per square meter, which subsequently has to be dried out by processing the print through a dryer station at elevated temperatures. This may be a severe energy requirement for a commercial diazotype development operation. In any event, having to apply large excesses of aqueous developer solutions to both sides of the support paper and dry it is an expensive, wasteful procedure.
The moist development process has been advocated for general office use because of the relative absence of odors generated. The need for evaporating circa 20 g/m.sup.2 of water at elevated temperatures however, is counterproductive to airconditioning in an air conditioned office. Moreover, the developer solutions tend to oxidize and become dark and have to be replaced frequently, combined with a thorough cleaning of the developer machine.
Recently a moist development process has been proposed (see U.S. Pat. No. 4,128,423) which remedies various shortcomings of the classical moist development process. By the new process one applies between 1.5 to 4.5 cm.sup.3 of developer per square meter, only to one side of the light-sensitived paper. This corresponds to from 2 to 6% of the average print weight. No print dryer is required. The developer is spread onto the print surface with the aid of a transfer roller, adapted to transfer 1.5 to 4.5 cm.sup.3 of developer per square meter of print surface. Conventionally coated one component diazotype papers would produce a pronounced curl when treated in this manner, as the water from the developer wets only one side of the print (see the discussion of this phenomenon given above). In order to overcome this phenomenon the U.S. Pat. No. 4,128,423 teaches the application of a special plastic sealer undercoat to the paper support. The sealer provides impermeability to water. The light sensitive diazo coating consists of a self contained layer with pigments and resin binders since it cannot anchor within the surface layer of the support. Upon development, the water of the developer solutions cannot penetrate into the paper fibers of the base and the print does not curl. It is also proposed to apply the sealer undercoat to both sides of the base to prevent curl from developer solution which may touch the backside of the print. Those skilled in the art appreciate that the application of a sealer undercoat is a delicate procedure and requires substantial coating weights to be effective. Since the sealer layer is hydrophobic and the light sensitive overcoating is hydrophylic, this latter layer must be carefully formulated and requires a substantial thickness and coating weight. Such coatings are difficult to apply successfully and conventional diazotype coating machines are not adapted to handle them. The special coating process increases the manufacturing costs of the diazo material far above those of conventionally coated, one component diazotypes.
It is an objective of the present invention to overcome the shortcomings described above, particularly as they relate to the moist development process and to provide a superior diazotype print product and a highly economic process. It is a further objective of the invention to provide a moist development process that can be practiced in any commercial processing equipment that permits the transfer and spread of from 0.6 to 4 g/m.sup.2 of developer liquid to a diazotype print surface.
The method of the invention is odorless. The developer components are non-volatile under the development process conditions and do not enter into the work atmosphere surrounding the printing apparatus. The developer solution of the invention employs a vehicle which does not swell the cellulosic fibers of the base paper, obviating the problem of curling of the developed print and a need for drying the developed print. Further, in the developer solutions of the invention, the ingredient buffer salts of amines or amino alcohols and low molecular weight organic acids are liquid oils or waxes which do not tend to crystallize or solidify as do alkali salts in prior art developer solutions.
The process of the present invention is also advantageous in that contrary to the amine development process, no "ghost" repeat images occur on transfer prints. Other advantages of the process of the invention will be described below.